A window regulator is used in a motor vehicle to transmit a drive force to a window in the motor vehicle. The window regulator includes a drive unit (such as a cable or a belt) connected to a drive device (such as a crank or a motor) that transmits a drive force to the window regulator. The window may be driven by slides that are moveable along tracks under the action of the cable. The cable may be split into a lower cable and an upper cable wound in opposite directions on a drum driven by the motor.
The tension in the cable in the window regulator must be effectively controlled. Slack in the cable leads to inaccuracy in the operation of the window regulator and inaccuracy in the position of the slides relative to the position of the drum. On the other hand, overtension in the cable can prematurely wear the window regulator components.
The operating accuracy of the window regulator is important, especially for a window regulator utilized in a frameless door. In certain models of window regulators used in frameless doors, the window lowers slightly when the door is opened to disengage from the roof seal. The window must therefore be moved accurately so that the opening of the door is not hindered. The movement must also not be too great to meet regulatory constraints, in particular anti-pinch regulations. There must therefore be sufficient tension in the window drive cable to ensure accurate movement of the window.
The components of the window regulator device are subject to gradual aging, which can lead to elongation of the cable due to, for example, wear on the driving drum and the pulleys, the compression of the cable sheaths, or creep in the pulleys. Cable elongation due to aging of the various parts of the window regulator must be compensated for.
Moreover, when the window is being raised, the drive motor still applies torque to the window regulator device when the window reaches its upper limit. The overtorque at the upper limit can cause elastic deformation of the window regulator components and cause elastic elongation of the cable and the other stressed units.
Play compensation mechanisms are employed to absorb the elongation of the cable and ensure sufficient tension for the correct operation of the window regulator device.
European patent application No. EP 0,244,303 discloses a play compensation mechanism including a tensioner screw and a nut compressed by a pusher and a flexible unit. In one direction, the screw helically moves in the nut under the axial thrust of the flexible unit when the force exerted by the pusher is removed or reduced. In the other direction, the screw cannot translate or rotate in the nut. This mechanism is an irreversible friction-based system. Thus, when play is likely to occur between two parts linked to the tensioner screw, the play is automatically compensated for when it appears due to the one-way movement of the screw relative to the screw.
However, this mechanism also compensates equally for elongation of the cable due to the aging of the window regulator device and for elastic deformation caused by the drive torque when the window regulator mechanism is at its upper limit. The elastic deformation, which appears the first time the window regulator is maneuvered to its upper limit, can be as much as 5 to 8 mm and is approximately constant during subsequent maneuvers. However, this deformation is eliminated when the drive torque is released.
The mechanism described in European Patent Application EP 0,244,303 compensates for elastic deformation, leading to overtension in the cable and premature deterioration of the cable. When there is overtension in the cable, the premature wear of the components in the mechanism deteriorates the window regulator mechanism after a few thousand cycles, whereas the target lifetime of the mechanism is several tens of thousands of cycles.
There is therefore a need for a cable tensioner in a window regulator device that can irreversibly compensate for elongation caused by wear and reversibly compensate for elastic deformation.